1. Field of the Invention
The present invention is directed to an apparatus for determining the partial pressure of a gas utilizing a double bored catheter whose outer tube is permeable to the gas, together with a pump for circulating a carrier fluid continuously through the space between the two tubes of the catheter, together with a measuring means for determining the partial pressure of the gas in the fluid.
2. Description of the Prior Art
Various types of apparatus for the determination of the partial pressure of gases and gas mixtures dissolved in fluids are used, for example, in medicine in the analysis of arterial blood and analysis of respiratory air. Other applications of such apparatus are to be found in environmental protection in the measurement of nitrous oxides in exhaust gases and in the measurement of the oxygen content of standing bodies of water. A still further example of the application of such apparatus is in the measurement of partial pressures in absorption processes such, for example, as in gas separating and in gas cleaning.
An apparatus of the type described will be found in German AS 25 34 255. In this known apparatus which is particularly intended for the determination of gas concentrations dissolved in blood, a catheter is introduced into the blood stream to be analyzed in the living subject. At least one part of the catheter is provided with a tubular membrane which is in direct contact with the blood, the tubular membrane being permeable by the gases and essentially impermeable by the blood. A gas which is admitted into the catheter at roughly atmospheric pressure thereby comes into contact with the membrane and is employed as a carrier fluid. After an equilibrium between the carrier gas and the gases dissolved in the blood has been established, the gas mixture is removed from the catheter and analyzed.
This known apparatus has a number of disadvantages. The use of gas as a carrier fluid represents a certain safety risk upon catheter failure, since the carrier gas can then proceed directly into the blood circulation. Furthermore, the known apparatus permits only a discontinuous measurement since one must wait first for the equilibrium between the carrier gas and the gases dissolved in the blood to be established and then a specimen can be removed from the catheter to be analyzed in a separate unit.